1. Field of the Invention
The present invention relates to a power-supply apparatus, and more particularly, to a power-supply apparatus able to operate in parallel with another power supply to provide a current-sharing mechanism and a current-sharing method thereof.
2. Description of the Related Art
Power supplies have been widely used in electronic apparatuses and other products to provide regulated power. FIG. 1 is a block diagram showing a conventional power supply. Referring to FIG. 1, the power supply includes a direct current (DC) unregulated input voltage VIN, a power circuit 10, an regulated DC output voltage VO, and a voltage divider formed by connecting resistors RA and RB in series. The power supply further comprises a feedback control circuit, which is coupled to the power circuit 10. The feedback control circuit comprises a control unit 20, an error amplifier 30, and a reference voltage VR. The regulated DC output voltage VO is coupled to the feedback control circuit via the voltage divider. The voltage divider is coupled from the regulated DC output voltage VO to a ground reference. A voltage-dividing junction between the resistors RA and RB is coupled to a negative terminal of the error amplifier 30. The reference voltage VR is coupled to a positive terminal of the error amplifier 30. An output terminal of the error amplifier 30 outputs a feedback signal to the control unit 20. The feedback control circuit regulates the feedback signal to control an output of the power supply. Regardless of load conditions or input voltage variations, the feedback signal is regulated so as to maintain a stable DC voltage of the power supply. In addition, the power circuit 10 can be a linear-type or a switching-type structure.
Serial buses, such as I2C or SM(smart buses), have been widely applied in personal computers and peripheral circuits for hardware monitoring. FIG. 2 is a block diagram showing connection of apparatuses through a serial bus in a conventional computer system. Referring to FIG. 2, the apparatuses transmit data through the serial bus, also known as the bus. For instance, the microprocessor is able to monitor a voltage of the battery and an on/off status of the power supply through the bus. Moreover, the microprocessor can access parameters such as the voltage, current, the fan speed, and the operating temperature of the power supply. FIG. 3 shows a timing diagram of the bus in FIG. 2. In the bus, the bus terminal DATA transmits data, and the clock terminal CLK indicates the validity of the data, such as logic levels VDH and VDL, from the bus terminal DATA. Accordingly, all apparatuses coupled to the bus can dominate the bus. Under normal situation, levels at the bus terminal DATA and the clock terminal CLK are logic-high. When the bus is transmitting data, levels at the bus terminal DATA and the clock terminal CLK are logic-low.
The conventional power supply cannot provide parallel output. For a system with a high current output and/or a fault tolerance system, parallel power supplies are required. To enhance the reliability, the parallel power supplies must have a current-sharing function to share the output current and to reduce the operating temperature of power supplies.